1. Technical Field of the Invention
The present invention relates to an automatic automobile headlamp leveling device for automatically adjusting the tilt of headlamps of a vehicle based on a tilt of the vehicle in a longitudinal direction thereof (hereinafter, referred to as pitch angle) in a direction in which the light axes of the headlamps are adjusted so as to offset the tilt of the vehicle (hereinafter, referred to as automatic leveling).
2. Background of the Prior Art
A headlamp of this kind is constructed, for instance, such that a reflector having a light source securely inserted thereinto is supported in such a manner as to be tilted about a horizontal tilting shaft relative to a lamp body and that the light axis of the reflector (headlamp) is tilted by an actuator about the horizontal tilting shaft.
A conventional automatic headlamp leveling device comprises a pitch angle detection means, a vehicle speed sensor and a control section for controlling the driving of actuators based on detection signals from the detection means and sensor, which are mounted on a vehicle for adjusting light axes of the headlamps of the vehicle such that the light axes stay in a certain state relative to the surface of a road at all times.
The conventional automatic headlamp leveling device is, however, constructed such that the leveling of headlamps of a vehicle is performed in real time, whether the vehicle is running or at a stop, in response to a change in vehicle posture. The change in vehicle posture may be caused by the acceleration or deceleration of the vehicle, or a change in load resulting from the loading or unloading of luggage, or when occupants get in or out of the vehicle. This causes the actuator to be activated a large number of times, thereby increasing power consumption; thus, high durability is required for the driving mechanism components, such as motors, gears and the like, and production costs are increased.
To cope with this problem, an automatic headlamp leveling device (Japanese Unexamined Patent Publication No. HEI 10-274859) was proposed with a view to providing an automatic headlamp leveling device that is inexpensive and which has a long service life by reducing the frequency at which the actuators are driven. The proposed automatic headlamp leveling device is constructed so that the driving of the actuators is controlled at certain intervals while the vehicle is at a stop, and when the vehicle is starting, the driving of the actuators is controlled based on latest pitch angle data from when the vehicle was at a stop (pitch angle data detected immediately prior to the start of the vehicle)
There is a drawback with the proposed automatic headlamp leveling device, however, in that the control of the driving of the actuators when the vehicle is starting is not performed accurately enough so that a proper automatic leveling is not proivded. This improper automatic headlamp leveling will be described with reference to FIG. 4.
FIG. 4 shows changes in vehicle speed and vehicle posture from when an accelerator pedal of a vehicle is depressed to start it running until the vehicle reaches a running at a constant speed. As shown therein, a predetermined time period (T) is required from when the accelerator pedal is depressed until the vehicle actually starts to run. In other words, the vehicle speed starts to increase during the predetermined time (T) after the accelerator pedal is depressed. On the other hand, as to the posture of the vehicle, since the acceleration is drastically put in action when the accelerator pedal is depressed, the vehicle hip dives and it restores its initial or normal posture when the vehicle speed becomes constant. Thus, when the vehicle speed sensor detects the start of the vehicle (when the control section detects the start of the vehicle based on an output from the vehicle speed sensor), the vehicle is in a hip dive state (a state in which the front of the vehicle is raised), and therefore, the pitch angle detecting means (a vehicle height sensor) detects a pitch angle of the vehicle, the front of which is being raised, and the leveling of the headlamps is performed such that the light axes of the headlamps are tilted downwardly based on that improper pitch angle.
The present invention was made in view of the aforesaid problem inherent in the previously proposed devices, and an object thereof is to provide an automatic automobile headlamp leveling device that is inexpensive and which has a long service life by reducing the frequency at which actuators are driven to thereby improve the improper automatic headlamp leveling when a vehicle is starting.
With a view to attaining the aforesaid object, the present invention provides an automatic automobile headlamp leveling device comprising headlamps each adapted to be driven by an actuator such that a light axis thereof is tilted up and/or down relative to a vehicle body, control means for controlling the driving of said actuators, vehicle speed detection means for detecting the vehicle speed, pitch angle detection means for detecting a pitch angle of the vehicle, and a storage section for storing pitch angle data of the vehicle detected by the pitch angle detection means. The control means controls the driving of the actuators based on pitch angle data detected by the pitch angle detection means such that the light axes of the headlamps always stay in a certain tilted state relative to the surface of a road, wherein the storage section is constructed so as to store a plurality of data ranging from latest pitch angle data to pitch angle data detected a predetermined time period prior to the latest data, and wherein the control means judges whether the vehicle is at a stop or is starting based on outputs from the vehicle speed sensors and then controls the driving of said actuator at certain intervals based on the latest pitch angle data when the vehicle is being at a stop. When the vehicle is starting, it controls the driving of the actuator based on pitch angle data detected immediately prior to the start of the vehicle, the automatic automobile headlamp leveling device being characterized in that pitch angle data detected prior to the depression of an accelerator pedal of the vehicle are used as the pitch angle data detected immediately prior to the start of the vehicle which data are to be used for controlling the driving of the actuator when the vehicle is starting.
The pitch angle data when the vehicle is at a stop is less affected by disturbance factors than the pitch angle data when the vehicle is running, and therefore the former is more accurate than the latter to that extent, and since the driving of the actuators are controlled based on these accurate pitch angle data, the automatic headlamp leveling so performed can be accurate to that extent.
In addition, since the controlling of the driving of the actuators is limited to an interval of a certain time period, the frequency at which the actuators are activated can be lowered to that extent, whereby the consumption of electric power can be saved and the wear of the driving mechanism components can also be reduced.
Furthermore, when the start of the vehicle is detected by the vehicle speed sensor, the actuators are driven based on accurate pitch angle data taken immediately prior to the start of the vehicle (when the vehicle is at a stop), whereby a proper automatic headlamp leveling can be performed.
To describe this in detail with reference to FIG. 4, pitch angle data detected within the time period T from when the accelerator pedal is depressed until the vehicle speed sensor detects the start of the vehicle are not necessarily proper since the vehicle hip dives. Thus, an automatic headlamp leveling is performed based on the latest pitch angle data which was detected immediately prior to the start of the vehicle when it was at a stop by using pitch angle data detected prior to that time period T (pitch angle data detected within a time period indicated by reference character A in FIG. 4), whereby an improper automatic headlamp leveling immediately after the start of the vehicle can be avoided.
The present invention provides an automatic automobile headlamp leveling device, wherein pitch angle data detected a predetermined time period prior to the detection of the start of the vehicle by the vehicle speed sensor while the vehicle is at a stop are used as the pitch angle data detected prior to the depression of the accelerator pedal. In addition, it is desirable to use pitch angle data detected during the predetermined time period which is set within a range from 1 to 3 seconds prior to the detection of the start of the vehicle by the vehicle speed sensor, while the vehicle is at a stop, as the pitch angle data detected prior to the depression of the accelerator pedal.
Although there is a slight difference from vehicle to vehicle, it generally takes 1 to 3 seconds until the vehicle actually starts to run after the accelerator pedal is depressed. In view of this, an automatic automobile headlamp leveling device of the present invention has the pitch angle data stored in the storage section replaced sequentially for data updating in such a manner that oldest pitch angle data are replaced with latest pitch angle data every time new pitch angle data are inputted.
With this construction, the pitch angle data detected during the predetermined time period before can be used at all times, and the capacity of the storage section does not have to be increased particularly.
In addition, in the automatic automobile headlamp leveling device of the present invention, the controlling of the actuator is performed provided that the headlamps are being turned on.
As long as the headlamps are not turned on, the actuators are not activated, and therefore the number of times when the actuators are activated can be reduced, whereby the consumption of electric power is saved and the wear of constituent members of the driving mechanism is also reduced.
In the automatic automobile headlamp leveling device of the present invention, the actuator driving intervals may be set so as to be longer than a maximum driving time of the actuator required for each leveling operation.
When an interval between a previous control and a control following the same is shorter than the maximum driving time of the actuator, the actuator starts the following operation before a target value is reached, and this increases the frequency at which the actuator is driven, whereby the life of the actuator is reduced. According to the construction of the present invention, however, only after the actuator reaches the target value through a previous control, the actuator is constructed to be driven through a control subsequent thereto, whereby the frequency at which the actuator is driven is reduced, thus increasing the life of the actuator.
Furthermore, since the change in pitch angle within an interval between the previous control to the control following the previous control can be omitted by increasing the interval, those two controls can be omitted without entailing the driving of the actuators. In other words, since all operations within the interval are directed to the driving of the actuators in the following control, the frequency at which the actuators are driven is reduced to that extent.
Moreover, the pitch angle data of the vehicle which are detected by the pitch angle detection means are taken into the control section at all times so that they are calculated as a control amount even during an interval between controls of the driving of the actuators, and all of the pitch angle data taken into the control section are used as control data, whereby so many pitch angles can be used as control data, so that a proper automatic headlamp leveling is made possible which results from the detection of accurate vehicle postures (pitch angles).